An inscribed gear type fluid pump, as shown in PTL 1 for instance, employs a combination of an inner rotor and an outer rotor having one more tooth than the inner rotor, with the inner and outer rotor being disposed with offset from each other. A pump rotor is formed generally by sintering. Thereafter, sizing is effected for correcting size and shape.
Such sizing of the pump rotor is effected normally with using a mold comprising a combination of a die, upper and lower punches and a core. In the course of this, as for the inner rotor for example, tooth flanks of outer teeth thereof are abraded (thrusted) by the die, which sometimes can result in reduction in the perpendicularity of the tooth flank of the pump rotor. The language “perpendicularity of the tooth flank” as used herein refers to perpendicularity relative to the end face. Ideally, the end face and the tooth flank form 90 degrees angle therebetween. With reduction in perpendicularity, there can occur instability in the discharging performance and/or the pulsating performance of the fluid pump. Although the perpendicularity of tooth flank can be corrected by e.g. polishing of the tooth flank after sizing, but as this involves the addition of correcting step, manufacturing cost increase will result. For this reason, in the case of the pump rotor described in PTL 1, rather than effecting correction of slope of tooth flank, direction of assembling the outer rotor with the inner rotor is specified, so that appropriate gap may be formed between respective tooth flanks, in an effort of stabilizing discharging performance and pulsating performance.